Center of curvature [1] The optical system composed of two or more refraction (or reflection) spheres on the same line is called Coaxial spherical system The line where the center of curvature is located is called the main optical axis of the optical system. For a single refractive sphere or spherical mirror, the main optical axis is a straight line connecting the spherical vertex (the midpoint of the spherical light receiving part) and its curvature center. The light beam is composed of light beams with certain relationship. Where all light beams (or their extension lines) in the beam intersect at the same point, the beam is called concentric beam. After the incident concentric beam passes through the ideal optical system, the outgoing beam must also be concentric. The intersection of incident concentric beams is called object point, and the intersection of outgoing concentric beams is called image point. Ideal optical system It has the following properties: ① A point (object point) on the object side of the optical system corresponds to a point (image point) on the image side.
That is, after all the incident light emitted from the object point passes through the optical system, the outgoing light is delivered to the image point. According to the principle of light reversibility, after all the light emitted from the original image point enters the optical system, all the outgoing light rays will be delivered to the original object point. The interchangeable point of this pair of objects and images is called the conjugate point. A certain incident ray and the corresponding outgoing ray are called conjugate rays.
② Each straight line of the object side corresponds to a straight line of the image side, which is called the conjugate line; Each plane of the object square corresponds to a plane of the image square, which is called total yoke noodles. ③ The conjugate point of any point on the main optical axis is still on the main optical axis.
The conjugate plane of any plane perpendicular to the main optical axis is still perpendicular to the main optical axis.
④ For the conjugate plane perpendicular to the main optical axis, the transverse magnification (see Convex lens ）Is a constant. The theory that studies the one-to-one correspondence between the above two objects and images in an ideal optical system is called Gaussian optics. Light is purely a geometric theory F. Gauss expounded in his 1841 book. There is no real Ideal optical system The plane mirror is an exception, but its transverse magnification is always 1. Coaxial spherical system Strictly speaking, it is not an ideal optical system, but it can approximately meet the requirements of an ideal optical system under paraxial conditions. The concept and theory of an ideal optical system are abstracted and summarized based on this prototype, so Gaussian optics is also called paraxial optics. stay [2] In the coaxial spherical system, if the incident light and the outgoing light are close to the main optical axis, and the included angle μ with the main optical axis is very small, so that sin μ ≈ tg μ ≈ μ, cos μ ≈ 1 are approximately true, the corresponding light is called paraxial light, and the above conditions are called paraxial conditions. The coaxial spherical system can be approximately regarded as Ideal optical system 。 
